Robert A. Schommer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert A. Schommer Observatory clear sky chart from 2005-11-06 to 2024-11-03.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	16% 7% 2 6% 4 4 4 4 5% 7% 39%	101293
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	97706
Transparency	Day	42% 7% 12% 22% 15% 2	101048
	Night	42% 6% 12% 22% 15% 2	97571
Seeing	Day	20% 15% 30% 23% 10% 3	15004
	Night	20% 12% 32% 27% 9% 1	24174

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	15% 7% 2 5% 3 4 4 3 4 4 47%	2517
	11th to 20th	Day	15% 9% 3 7% 5% 4 5% 4 5% 7% 36%	2520
	21st to end	Day	23% 11% 4 7% 4 4 4 3 4 5% 34%	3070
February	1st to 10th	Day	16% 7% 3 7% 5% 4 4 3 5% 6% 40%	1710
	11th to 20th	Day	15% 8% 2 7% 3 4 4 3 4 6% 42%	1842
	21st to end	Day	19% 8% 2 7% 4 4 3 4 5% 5% 38%	1570
March	1st to 10th	Day	27% 8% 2 5% 4 3 3 3 4 5% 36%	3116
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 8% 45%	3380
	21st to end	Day	21% 6% 2 6% 3 3 3 3 4 5% 43%	4102
April	1st to 10th	Day	17% 8% 3 7% 4 4 4 4 5% 6% 39%	2280
	11th to 20th	Day	16% 7% 2 6% 4 4 3 4 6% 8% 41%	2254
	21st to end	Day	18% 6% 2 5% 4 4 4 3 6% 6% 40%	2280
May	1st to 10th	Day	26% 9% 2 6% 4 4 4 3 5% 7% 29%	4096
	11th to 20th	Day	25% 8% 3 7% 5% 5% 4 3 5% 6% 30%	4391
	21st to end	Day	13% 6% 2 5% 4 4 4 3 7% 9% 43%	4837
June	1st to 10th	Day	14% 5% 2 6% 5% 5% 5% 4 6% 10% 37%	2660
	11th to 20th	Day	13% 7% 2 6% 6% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	11% 6% 2 6% 5% 6% 6% 4 5% 8% 40%	2660
July	1st to 10th	Day	8% 6% 3 8% 6% 6% 6% 5% 7% 10% 35%	4440
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 9% 38%	4440
	21st to end	Day	13% 8% 3 8% 6% 5% 6% 5% 7% 8% 30%	4814
August	1st to 10th	Day	19% 6% 2 7% 5% 5% 4 4 6% 9% 31%	4115
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 9% 40%	3730
	21st to end	Day	11% 5% 2 5% 3 4 4 4 5% 8% 48%	4180
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 5% 6% 45%	2280
	11th to 20th	Day	13% 6% 2 4 3 4 3 3 5% 8% 49%	2214
	21st to end	Day	19% 6% 3 5% 4 5% 4 4 5% 6% 39%	2090
October	1st to 10th	Day	19% 7% 2 5% 3 4 5% 4 4 6% 41%	1958
	11th to 20th	Day	14% 6% 2 4 3 3 4 3 6% 6% 48%	1900
	21st to end	Day	18% 6% 2 5% 3 4 4 3 5% 6% 45%	1967
November	1st to 10th	Day	15% 6% 2 5% 3 3 3 2 4 6% 51%	1689
	11th to 20th	Day	17% 6% 2 5% 3 2 3 3 6% 5% 47%	1710
	21st to end	Day	16% 6% 2 4 4 4 4 3 5% 7% 45%	1623
December	1st to 10th	Day	18% 8% 3 5% 4 3 3 3 6% 7% 38%	1520
	11th to 20th	Day	20% 7% 2 4 4 3 4 3 5% 6% 43%	1906
	21st to end	Day	18% 7% 3 6% 5% 5% 5% 4 6% 6% 33%	2772
January	1st to 10th	Night	16% 7% 2 5% 3 3 4 3 5% 6% 46%	4429
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 4 6% 42%	4440
	21st to end	Night	24% 10% 3 6% 3 3 3 3 4 5% 35%	4582
February	1st to 10th	Night	17% 9% 2 5% 4 3 4 3 5% 6% 41%	2470
	11th to 20th	Night	17% 9% 3 6% 4 4 3 3 5% 5% 41%	2223
	21st to end	Night	20% 7% 2 5% 3 3 4 3 4 6% 43%	1884
March	1st to 10th	Night	24% 10% 3 5% 4 3 3 3 3 5% 37%	3724
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 7% 48%	3575
	21st to end	Night	20% 8% 3 5% 4 3 3 2 3 4 43%	3530
April	1st to 10th	Night	18% 6% 3 6% 4 4 4 4 5% 7% 38%	1900
	11th to 20th	Night	17% 8% 2 6% 4 5% 4 3 5% 7% 40%	1875
	21st to end	Night	19% 6% 2 5% 3 3 4 3 5% 7% 42%	1900
May	1st to 10th	Night	25% 8% 3 8% 4 4 3 3 4 8% 29%	2844
	11th to 20th	Night	25% 8% 3 7% 4 4 3 3 4 6% 32%	2530
	21st to end	Night	15% 7% 2 6% 4 3 4 4 5% 9% 41%	2738
June	1st to 10th	Night	16% 6% 2 6% 4 3 3 4 6% 9% 42%	1520
	11th to 20th	Night	12% 7% 2 6% 4 5% 5% 4 6% 9% 40%	1520
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 7% 11% 41%	1520
July	1st to 10th	Night	8% 6% 2 8% 5% 6% 5% 5% 7% 10% 38%	2520
	11th to 20th	Night	13% 6% 2 6% 5% 4 5% 5% 7% 11% 36%	2520
	21st to end	Night	15% 8% 3 7% 5% 4 5% 5% 7% 8% 35%	2739
August	1st to 10th	Night	23% 6% 3 6% 5% 5% 5% 4 6% 8% 31%	2777
	11th to 20th	Night	14% 6% 2 7% 4 4 5% 4 7% 7% 39%	3097
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	3476
September	1st to 10th	Night	14% 6% 3 7% 4 5% 5% 3 5% 6% 44%	1900
	11th to 20th	Night	13% 6% 2 4 3 3 3 3 5% 7% 51%	1965
	21st to end	Night	18% 7% 2 6% 4 4 3 3 4 7% 42%	2090
October	1st to 10th	Night	18% 7% 2 6% 4 3 4 4 5% 5% 44%	2218
	11th to 20th	Night	14% 4 2 5% 4 3 3 3 4 6% 51%	2280
	21st to end	Night	18% 7% 3 5% 3 3 3 3 5% 5% 46%	2629
November	1st to 10th	Night	12% 6% 2 5% 3 4 4 3 4 5% 53%	2434
	11th to 20th	Night	18% 6% 2 5% 3 3 3 3 4 5% 47%	2470
	21st to end	Night	14% 7% 2 4 4 4 3 3 6% 7% 46%	2555
December	1st to 10th	Night	20% 7% 2 6% 4 3 4 3 5% 6% 40%	2660
	11th to 20th	Night	19% 6% 2 5% 3 3 4 4 6% 6% 42%	3288
	21st to end	Night	19% 9% 3 6% 5% 4 4 3 4 5% 37%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	38% 6% 11% 28% 13% 3	2518
	11th to 20th	Day	46% 6% 11% 21% 14% 2	2520
	21st to end	Day	53% 6% 9% 21% 10% 2	3070
February	1st to 10th	Day	45% 5% 13% 23% 12% 2	1710
	11th to 20th	Day	45% 5% 9% 23% 16% 3	1851
	21st to end	Day	48% 5% 10% 21% 13% 4	1570
March	1st to 10th	Day	49% 6% 10% 24% 9% 2	3119
	11th to 20th	Day	33% 7% 13% 29% 15% 3	3380
	21st to end	Day	43% 5% 8% 17% 22% 5%	4102
April	1st to 10th	Day	44% 6% 9% 20% 15% 5%	2280
	11th to 20th	Day	40% 6% 13% 21% 17% 3	2254
	21st to end	Day	42% 7% 10% 19% 18% 4	2280
May	1st to 10th	Day	54% 6% 12% 15% 11% 2	4110
	11th to 20th	Day	53% 7% 13% 17% 9% 1	4395
	21st to end	Day	35% 8% 13% 24% 18% 2	4837
June	1st to 10th	Day	40% 8% 13% 21% 15% 2	2660
	11th to 20th	Day	42% 9% 14% 22% 12% 2	2660
	21st to end	Day	39% 9% 13% 22% 16% 1	2660
July	1st to 10th	Day	41% 11% 14% 19% 14% 1	4370
	11th to 20th	Day	39% 10% 16% 21% 14% 1	4365
	21st to end	Day	47% 9% 12% 16% 15% 1	4661
August	1st to 10th	Day	47% 9% 14% 20% 9% 1	4101
	11th to 20th	Day	38% 8% 14% 26% 13% 1	3766
	21st to end	Day	32% 7% 11% 26% 22% 2	4180
September	1st to 10th	Day	38% 8% 11% 20% 20% 3	2280
	11th to 20th	Day	33% 6% 11% 23% 23% 3	2214
	21st to end	Day	45% 6% 9% 17% 19% 3	2090
October	1st to 10th	Day	42% 7% 12% 19% 18% 2	1958
	11th to 20th	Day	35% 5% 10% 25% 22% 2	1900
	21st to end	Day	40% 5% 11% 23% 19% 2	1967
November	1st to 10th	Day	35% 4 12% 25% 21% 2	1689
	11th to 20th	Day	38% 5% 9% 23% 22% 3	1710
	21st to end	Day	38% 4 13% 30% 12% 3	1623
December	1st to 10th	Day	45% 5% 15% 21% 13% 1	1520
	11th to 20th	Day	42% 7% 13% 25% 12% 2	1906
	21st to end	Day	47% 7% 12% 24% 10% 1	2772
January	1st to 10th	Night	39% 5% 11% 30% 12% 4	4429
	11th to 20th	Night	44% 4 12% 25% 12% 3	4440
	21st to end	Night	50% 6% 9% 22% 12% 2	4582
February	1st to 10th	Night	43% 6% 13% 24% 13% 2	2470
	11th to 20th	Night	44% 4 10% 19% 18% 5%	2225
	21st to end	Night	43% 4 9% 23% 17% 4	1884
March	1st to 10th	Night	50% 4 9% 22% 11% 3	3734
	11th to 20th	Night	35% 8% 13% 25% 17% 2	3576
	21st to end	Night	45% 5% 7% 15% 22% 6%	3530
April	1st to 10th	Night	44% 7% 10% 19% 17% 4	1900
	11th to 20th	Night	44% 6% 9% 19% 20% 2	1875
	21st to end	Night	40% 6% 10% 21% 19% 4	1900
May	1st to 10th	Night	53% 7% 11% 17% 10% 1	2850
	11th to 20th	Night	52% 7% 14% 14% 10% 2	2531
	21st to end	Night	38% 8% 15% 22% 14% 3	2739
June	1st to 10th	Night	39% 7% 12% 21% 19% 2	1520
	11th to 20th	Night	39% 8% 15% 25% 12% 1	1520
	21st to end	Night	36% 9% 15% 24% 14% 1	1520
July	1st to 10th	Night	40% 10% 17% 19% 12% 2	2480
	11th to 20th	Night	39% 10% 15% 23% 12% 1	2472
	21st to end	Night	44% 8% 16% 16% 15% 2	2651
August	1st to 10th	Night	49% 8% 17% 16% 8% 1	2767
	11th to 20th	Night	40% 8% 12% 27% 12% 1	3127
	21st to end	Night	31% 7% 11% 29% 21% 1	3476
September	1st to 10th	Night	40% 7% 11% 21% 19% 2	1900
	11th to 20th	Night	33% 5% 11% 23% 24% 4	1965
	21st to end	Night	42% 6% 7% 21% 21% 2	2090
October	1st to 10th	Night	41% 6% 12% 23% 16% 2	2218
	11th to 20th	Night	34% 5% 13% 27% 19% 3	2280
	21st to end	Night	40% 5% 10% 24% 19% 2	2629
November	1st to 10th	Night	34% 5% 11% 23% 23% 4	2434
	11th to 20th	Night	40% 5% 8% 24% 19% 5%	2470
	21st to end	Night	38% 4 14% 27% 16% 1	2555
December	1st to 10th	Night	45% 5% 12% 23% 13% 2	2660
	11th to 20th	Night	41% 7% 12% 21% 17% 4	3288
	21st to end	Night	47% 6% 12% 23% 11%	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	22% 24% 33% 16% 3 1	180
	11th to 20th	Day	26% 34% 26% 12% 1	180
	21st to end	Day	22% 25% 33% 14% 4 1	284
February	1st to 10th	Day	27% 24% 36% 10% 2	270
	11th to 20th	Day	25% 24% 39% 11% 2	450
	21st to end	Day	28% 22% 29% 18% 3	382
March	1st to 10th	Day	23% 26% 31% 17% 3	460
	11th to 20th	Day	23% 26% 33% 14% 4 1	460
	21st to end	Day	27% 22% 32% 14% 4 1	506
April	1st to 10th	Day	26% 22% 33% 13% 6% 1	460
	11th to 20th	Day	21% 23% 33% 13% 8% 2	452
	21st to end	Day	26% 20% 31% 17% 4 2	460
May	1st to 10th	Day	29% 18% 29% 16% 5% 2	463
	11th to 20th	Day	21% 14% 34% 22% 8% 1	487
	21st to end	Day	20% 8% 25% 29% 16% 3	529
June	1st to 10th	Day	16% 10% 32% 28% 12% 2	490
	11th to 20th	Day	16% 11% 30% 29% 12% 2	490
	21st to end	Day	15% 8% 34% 29% 13% 2	490
July	1st to 10th	Day	11% 6% 26% 32% 20% 6%	485
	11th to 20th	Day	9% 5% 25% 35% 21% 5%	484
	21st to end	Day	12% 7% 28% 33% 16% 3	532
August	1st to 10th	Day	11% 6% 22% 37% 17% 6%	486
	11th to 20th	Day	13% 4 22% 35% 22% 5%	479
	21st to end	Day	12% 7% 26% 31% 16% 8%	539
September	1st to 10th	Day	16% 9% 27% 24% 17% 7%	490
	11th to 20th	Day	14% 7% 26% 30% 14% 9%	490
	21st to end	Day	24% 11% 25% 25% 10% 4	490
October	1st to 10th	Day	25% 7% 25% 23% 14% 6%	490
	11th to 20th	Day	17% 14% 31% 25% 11% 3	490
	21st to end	Day	21% 15% 31% 21% 9% 2	474
November	1st to 10th	Day	15% 16% 32% 22% 13% 2	371
	11th to 20th	Day	23% 19% 31% 20% 6% 1	370
	21st to end	Day	18% 19% 35% 18% 8% 1	283
December	1st to 10th	Day	23% 28% 30% 11% 7% 1	180
	11th to 20th	Day	33% 21% 29% 12% 4	180
	21st to end	Day	25% 19% 34% 15% 6% 1	198
January	1st to 10th	Night	20% 20% 39% 18% 3	760
	11th to 20th	Night	25% 17% 35% 20% 3	760
	21st to end	Night	19% 20% 39% 21% 1	836
February	1st to 10th	Night	22% 17% 36% 23% 1	760
	11th to 20th	Night	25% 22% 38% 14% 1	743
	21st to end	Night	26% 20% 34% 18% 2	628
March	1st to 10th	Night	24% 18% 34% 20% 4	760
	11th to 20th	Night	24% 20% 34% 18% 4	760
	21st to end	Night	22% 14% 41% 18% 5%	836
April	1st to 10th	Night	22% 20% 36% 19% 4	760
	11th to 20th	Night	20% 15% 38% 22% 5%	751
	21st to end	Night	21% 13% 37% 25% 4 1	760
May	1st to 10th	Night	24% 14% 33% 22% 6%	580
	11th to 20th	Night	22% 8% 35% 28% 6%	396
	21st to end	Night	17% 6% 25% 38% 12% 2	411
June	1st to 10th	Night	17% 7% 29% 36% 11% 1	380
	11th to 20th	Night	13% 6% 30% 39% 12%	380
	21st to end	Night	8% 4 29% 47% 11% 1	380
July	1st to 10th	Night	11% 4 26% 42% 17% 2	370
	11th to 20th	Night	11% 4 22% 43% 19% 1	368
	21st to end	Night	10% 3 27% 43% 16%	416
August	1st to 10th	Night	13% 3 19% 45% 18% 2	532
	11th to 20th	Night	14% 3 19% 39% 23% 2	750
	21st to end	Night	15% 4 17% 41% 20% 2	836
September	1st to 10th	Night	16% 3 27% 34% 18% 2	760
	11th to 20th	Night	15% 5% 22% 32% 21% 4	760
	21st to end	Night	21% 6% 23% 33% 14% 1	760
October	1st to 10th	Night	22% 8% 27% 26% 14% 3	760
	11th to 20th	Night	16% 12% 30% 32% 10%	760
	21st to end	Night	23% 11% 32% 26% 8%	836
November	1st to 10th	Night	15% 11% 36% 27% 11% 1	749
	11th to 20th	Night	21% 16% 32% 24% 7%	760
	21st to end	Night	17% 17% 36% 23% 6% 1	760
December	1st to 10th	Night	27% 16% 32% 18% 6% 1	760
	11th to 20th	Night	22% 15% 38% 22% 4	760
	21st to end	Night	24% 15% 36% 23% 2	836

Page generated at 2024-10-31 03:39:23. Version ac07

Copyright © 2024 Attilla Danko.